Formation of Perfluoroalkyl Fullerene Alkylphosphonic Acid Self-Assembled Monolayers on Aluminum Oxide

Abstract

The possibility of fabricating self-assembled monolayers (SAMs) from alkylphosphonic acids functionalized with trifluoromethyl derivatives of C 60 on a metal oxide surface has been demonstrated in this work. Using several trifluoromethylfullerenes (TMFs) of different compositions and isomeric structures, we explored their relative reactivities in the Bingel-Hirsch cycloaddition reactions with 11-(diethoxyphosphoryl)undecyl methyl malonate for the first time. Only two isomers of C 60 (CF 3 ) 10 showed fairly selective monoadduct formation, whereas compounds with lower CF 3 content showed no selectivity. Converting the phosphonic ester into a phosphonic acid moiety enabled the successful formation of self-assembled monolayers of the TMF-alkylphosphonic acid on aluminum oxide surfaces. Considerable progress has been made in the past decade on the synthesis, purification and fundamental properties of perfluoroalkyfullerenes (PFAFs); their potential applications span the fields of organic electronics, imaging of biological objects, and energy conversion devices.1 Incorporation of PFAFs in organic optoelectronic devices may be carried out using solution processing, or vapor deposition, enabled by improved solubility and thermal stability compared to commonly used organofullerenes. In this work, the formation of self-assembled monolayers (SAMs) of PFAF functionalized alkylphosphonic acids on aluminum oxide surfaces has been probed for the first time.Use of SAMs for modification of electrical properties of various inorganic substrates has been proven as an effective method that may lead to improved conductivity and overall performance of organic optoelectronic devices.2 For example, one-dimensional metal oxide (MO x ) nanostructures show promise as new components in high-tech electronics.3 However, MO x nanostructures suffer from substandard charge transfer across the particle/particle interfaces, so mainstream application has yet to be achieved. Tunable electron acceptors have been attached to ZnO nanorods in the form of self-assembled monolayers (SAMs) in order to tune the electrical properties of the ZnO nanostructures. [4][5][6] The Halik group has shown that a SAM with C 60 -acceptor units can accept and accumulate electronic charges when incorporated into organic thin-film memory transistors. 5 The C 60 derivatives that differed by alkyl linkers of different chain lengths were synthesized and formed SAMs on the surface of ZnO nanorods with different insulating properties to tune the electrical properties of ZnO nanorods. 6 The electron withdrawing C 60 moiety was able to electronically couple with ZnO and as a result, the electrical performance of ZnO nanorods was improved. Further performance optimizations on SAM modified ZnO nanorods, and other MO x such as AlO x , require more efficient electron transfer and longer lifetimes of the reduced C 60 moiety. Attractive candidate materials that may fulfill these prerequisites are PFAFs, which not only exhibit superior electron acceptor properties, but also possess che...

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

“…In spite of the low X-ray scattering contrast between different polymers and organic materials, the obtained SLD profile between the polymer matrix and the fullerene allows the determination of the distribution of components and correlate it with the electronic properties. For example, the use of growth interruptions and the deposition rate to manipulate the phase separation mechanism [213]; the correlation and balance between the miscibility and optoelectronic properties of polymer-fullerene solar cells [214]; the formation of SAM of functionalized fluorinated alkyl fullerenes on aluminum oxide surfaces [215]; the development of unidimensional fullerene channels along the π-stacking direction of the polymer crystallites during doctor blading with subsequent controlled polymer drying [216]; and the alignment of the C 60 head groups within the SAM tuned by the alkyl phosphonic acids chain length [217], etc. In situ measurements also revealed a previously unknown mechanism of how additives can influence the polymer: fullerene bulk-heterojunction microstructure formation [218].…”

Trifluoromethyl‐Directed Supramolecular Self‐Assembly of Fullerenes: Synthesis, Characterization and Photovoltaic Applications

“…The compounds to form self‐assembly having π‐conjugated components are required for designing the optoelectronics devices . A well‐defined self‐assembly of the π‐conjugated molecule directly influences the performance of devices .…”